(1) Field of the Invention
The present invention relates generally to monitoring the level of a liquid and more particularly to an apparatus for monitoring the liquid level by measuring differential pressure thereof.
(2) Description of the Prior Art
Transmitters intended for liquid level monitoring have been manufactured for years. A variety of designs, ranging from electronic to pneumatic arrangements, have been used. Electronic differential pressure cell transmitters are designed to measure differential pressures within an enclosure. Although these devices have accurate high pressure range capabilities, they are limited by their large size and are capable of monitoring liquid levels only on the order of inches of the liquid column, and require electrical power at the detector location. These prior art limitations greatly inhibit the use of such devices by the chemical or nuclear industries, and in the medical field where liquid level monitoring on a much smaller scale is required. Furthermore, in many applications, it is not feasible or safe to have electric power in the vicinity of the level detector.
With the advent of optical fiber technology and the subsequent numerous applications to optical fiber sensors, several designs have been proposed for liquid level measurement. Some of the salient considerations over the previous art include better sensitivity, design versatility, and freedom from electromagnetic interference. To date, optical fiber liquid level sensors have typically been limited to switches, indicating the presence of a liquid, and not to devices for measuring a continuous range of liquid levels.